u-boot: support custom u-boot.bin name

On some platforms, the standard U-Boot binary is not called u-boot.bin,
but u-boot<something>.bin. This is for example the case on the
Cavium-provided u-boot, where the output file is called
u-boot_<boardname>.bin.

This patch adds a 'custom format' choice in the existing u-boot binary
format selection, where this name can be put. In the Cavium example, this
option could be set to:
BR2_TARGET_UBOOT_FORMAT_CUSTOM_NAME="u-boot-$(BR2_TARGET_UBOOT_BOARDNAME).bin"

Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

boot/uboot/Config.in

@@ -101,8 +101,24 @@ config BR2_TARGET_UBOOT_FORMAT_LDR
 config BR2_TARGET_UBOOT_FORMAT_ELF
 	bool "u-boot.elf"
 
+config BR2_TARGET_UBOOT_FORMAT_CUSTOM
+	bool "Custom (specify below)"
+	help
+	  On some platforms, the standard U-Boot binary is not called
+	  u-boot.bin, but u-boot<something>.bin. If this is your case,
+	  you should select this option and specify the correct name
+	  in BR2_TARGET_UBOOT_FORMAT_CUSTOM_NAME.
+
 endchoice
 
+config BR2_TARGET_UBOOT_FORMAT_CUSTOM_NAME
+	string "U-Boot binary format: custom name"
+	depends on BR2_TARGET_UBOOT_FORMAT_CUSTOM
+	help
+	  Specify the correct name of the output binary created by
+	  U-Boot, if it is not one of the default names. For example:
+	  u-boot_magic.bin
+
 config BR2_TARGET_UBOOT_OMAP_IFT
 	depends on BR2_TARGET_UBOOT_FORMAT_BIN
 	depends on BR2_arm || BR2_armeb

boot/uboot/uboot.mk

@@ -40,6 +40,8 @@ else ifeq ($(BR2_TARGET_UBOOT_FORMAT_NAND_BIN),y)
 UBOOT_BIN          = u-boot-nand.bin
 else ifeq ($(BR2_TARGET_UBOOT_FORMAT_IMG),y)
 UBOOT_BIN          = u-boot.img
+else ifeq ($(BR2_TARGET_UBOOT_FORMAT_CUSTOM),y)
+UBOOT_BIN          = $(call qstrip,$(BR2_TARGET_UBOOT_FORMAT_CUSTOM_NAME))
 else
 UBOOT_BIN          = u-boot.bin
 UBOOT_BIN_IFT      = $(UBOOT_BIN).ift